Active surveillance characterizes human intratumoral T cell exhaustion

Intratumoral T cells that might otherwise control tumors are often identified in an "exhausted" state, defined by specific epigenetic modifications and upregulation of genes such as CD38, cytotoxic T-lymphocyte-associated protein 4 (CTLA4), and programmed cell death 1 (PD1). Although the term might imply inactivity, there has been little study of this state at the phenotypic level in tumors to understand the extent of their incapacitation. Starting with the observation that T cells move more quickly through mouse tumors the longer they reside there and progress toward exhaustion, we developed a nonstimulatory, live-biopsy method for the real-time study of T cell behavior within individual patient tumors. Using 2-photon microscopy, we studied native CD8+ T cell interaction with antigen-presenting cells (APCs) and cancer cells in different microniches of human tumors and found that T cell speed was variable by region and by patient and was inversely correlated with local tumor density. Across a range of tumor types, we found a strong relationship between CD8+ T cell motility and the exhausted T cell state that corresponded with our observations made in mouse models in which exhausted T cells moved faster. Our study demonstrates T cell dynamic states in individual human tumors and supports the existence of an active program in "exhausted" T cells that extends beyond incapacitating them.